There are many commonly needed functions in a transmitter digital front-end, each requiring phase rotation of an in-phase/quadrature phase (I/Q) signal. Such functions are frequency correction of the signal, mixing of the signal to intermediate frequency, phase correction according to signal amplitude level (AM/PM) correction in pre-distortion functions, and conversion of PM signal to a constant envelope phase modulated I/Q signal in a polar transmitter, for instance.
Accurate I/Q vector rotations are computationally heavy operations and thus require a considerable amount of silicon area and power.